1. Field of the Invention
The present invention is directed to a method for self-adjustment of a triaxial acceleration sensor and a sensor system having a three-dimensional acceleration sensor during operation.
2. Description of Related Art
Micromechanical acceleration sensors are known, and are widely used in particular as acceleration or rotational rate sensors. The sensors must be adjusted to their field of application, using the higher-order process control system. The adjustment is usually carried out with a certain level of effort at the end of the manufacturing process by accelerating the sensor in its sensitive spatial axis, for all sensor axes in succession. These types of sensors have the disadvantage that a drift from the zero point and sensitivity during operation are not taken into account. Another approach is the use of the gravitational vector as a reference for an adjustment during operation, described in Loetters et al.: “Procedure for in-use calibration of triaxial accelerometers in medical applications,” Sensors and Actuators A 68 (1998), 221-228. A method therein is based on the fundamental principle that the sensor on a patient is not constantly accelerated, but instead has rest phases in which the acceleration of gravity may be used for the calibration. The method essentially uses the following method steps, not necessarily in the order stated:                ensuring the observability of the sensitivity and the offset;        calibrating the sensor with the aid of calibration values for sensitivity and offset;        checking the self-adjustment for an interfering acceleration, with the aid of a measurement equation and estimated values for sensitivity and offset;        repeating the adjustment if an interfering acceleration is recognized;        accepting the estimated values for sensitivity and offset as calibration values if an interfering acceleration is not recognized.        
Ensuring the observability of the sensitivity and the offset of the sensor means the recognition of a time interval which may be a candidate for a rest phase, so that sensitivity and offset may be determined as calibration values from the measured data. According to Loetters et al., the use of various filters ensures the observability and recognition of an interfering acceleration. One disadvantage of this method is that the filters in particular must be adapted to the product scenario, for example with respect to cut-off frequencies. This requires additional modeling, and limits the sensor to the particular scenarios. Loetters et al. use a sensor system having a three-dimensional acceleration sensor, a computing unit, and a memory, the computing unit being designed to carry out a calibration of the acceleration sensor during operation.